The team cloned the so-called RGA2 gene from the wild progenitor of edible bananas, Musaacuminata ssp. Malaccensis, which has a remarkable resistance to TR4. One modified Cavendish line (RGA2-3) remained TR4-free for the three years of the trial.

The disease-resistant RGA2-3 Cavendish banana plant in the lab.

Three other lines modified with RGA2 showed strong resistance, with 20% or fewer plants exhibiting disease symptoms over a period of three years. In contrast, 67% to 100% of the control bananas were either dead or heavily TR4-infected after three years, including the Giant Cavendish somaclonal variant 218, currently heralded as being resistant to TR.4.

Running from 2012 to 2015, the field trial was led by Distinguished Professor James Dale from Queensland University of Technology. It was conducted on a commercial banana plantation outside Humpty Doo in the Northern Territory in Australia previously affected by TR4. The soil was also heavily reinfested with disease for the trial.

Absolute breakthrough

The research team of Gert Kema, professor in tropical phytopathology at Wageningen University & Research, partnered in the project. “The GM banana lines show that the activity of the RGA2 gene is strongly correlated with the level of resistance to TR4,” comments Kema. “This is an absolute breakthrough as it concerns the first identified resistance gene to Fusarium wilt.”

“However,” says Kema, “this is only the start – some light at the end of the tunnel. The next step is to deploy the immense diversity in wild bananas to diversify the fruit and establish a resilient and sustainable banana production for all. In 2012, we determined that this banana species has valuable resistance to TR4 and Professor Dale’s group has now confirmed this by cloning the underlying gene. Our role was to validate the fungal infections using the molecular techniques that we developed to detect and quantify TR4.”

The TR4-resistant RGA2-3 Cavendish banana plant in the field.

Further research

While Cavendish bananas have been found to also have this RGA2 gene naturally, it is not very active in susceptible plants. New research is looking at how to ‘switch on’ the gene in Cavendish bananas to make them TR4 resistant.

The researchers have begun an expanded field trial on the same plantation, growing the four resistant RGA2 lines and newly developed lines of modified Grand Nain and Williams Cavendish varieties. They have the capacity to screen up to 9,000 plants for resistance and to determine yields and other important traits over the coming five years.

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